1. Field of the Invention
The present invention generally relates to semiconductor devices and methods for producing the same, and more particularly to a semiconductor device and a method for producing the semiconductor device, in which electrodes provided on a semiconductor substrate are respectively connected to protruding electrodes via barrier metal structure.
In recent years, with increasing demand for miniaturized semiconductor devices, a flip-chip type semiconductor device, which uses protruding electrodes such as bumps severing as connecting terminals, has attracted considerable attention.
The semiconductor device, on the other hand, is requested to have high reliability, and for this reason it is necessary to produce the protruding electrodes with the high reliability.
2. Description of the Related Art
FIG. 1 shows a conventional semiconductor device 1 with common protruding electrodes. As shown in this diagram, the semiconductor device 1 includes a plurality of electrode pads 3 on a circuit-forming surface of a semiconductor chip 2 thereof, and a plurality of bumps 4 are respectively provided on these electrode pads 3.
FIG. 2 is an enlarged diagram showing the electrode pad 3 and other parts therearound of the semiconductor device 1. As shown in this diagram, the bump 4 is not mounted directly on the electrode 3 but is connected thereto via a barrier metal structure 10 which is provided thereon. A detailed description of FIG. 2 is now given as follows.
The circuit-forming surface is protected by an insulating layer 6 formed thereon. The insulating layer 6 includes an aperture 7 designed in a position where the electrode 5 is formed, wherein the aperture 7 exposes the part of the circuit-forming surface on which the electrode 5 is to be formed.
The barrier metal structure 10 is configured to be a deposited structure consisting of three deposited layers: a first conductive metal layer 11, a second conductive metal layer 12 and a third conductive metal layer 13. Such a barrier metal structure 10 severs to prevent the metal element constituting solder bump 4 from causing a diffusion into the electrode pad 3. Specifically, since the bump 4 is an alloy of various metal elements, when the solder bump 4 is directly soldered to the electrode 5, the metal elements therein may penetrate into the electrode 5 by way of diffusion. This brings about a problem that the durability of the electrode pad 3 declines and thereby the brittle bump 4 may be detached from the electrode pad 3. Accordingly, the barrier metal structure 10 is provided just for eliminating the problem.
The first conductive metal layer 11, an undermost layer of the barrier metal structure 10, may be made of a material having a good adherence property with the electrode pad 3. The second conductive metal layer 12, deposited on the first conductive metal layer 11, may be made of a material having a good adherence with the first conductive metal layer 11. The third conductive metal layer 13, deposited on the second conductive metal layer 12, may be made of a material having not only a property of adhering to the second conductive metal layer 12 and to the bump 4 but also a property of preventing the diffusion of the metal elements in the bump 4.
The barrier metal structure 10 is formed in the following manner. First, the first conductive metal layer 11 is formed on the semiconductor chip 2 so as to cover the electrode pad 3. Second, the second conductive metal layer 12 is deposited on the first conductive metal layer 11 and then a resist having an opening corresponding to a predetermined shape of the barrier metal structure 10 is formed thereon. Third, in a state of the presence of the resist, the third conductive metal layer 13 is deposited on the second conductive metal layer 12. Finally, by removing the resist and unwanted parts of the first and second conductive metal layers 11 and 12, the barrier metal structure 10 is formed.
Meanwhile, the material used for forming the second conductive metal layer 12 is required to have a good adherence with respect to both of the first and third conductive metal layers 11 and 13. For this reason, the degree of freedom in selecting the material for the second conductive metal layer 12 is limited. Conventionally, in order to mainly meet the priority of requirement of adherence, a material inferior in terms of resistance to diffusion and oxidation, has to be used for the second conductive metal layer 12.
Further, it should be noted that the conventional barrier metal structure 10 is configured such that the second conductive metal layer 12 exposes its side wall surface. This brings about the problem that, during the forming of the bump 4, the material forming the bump 4 may have contacted with the exposed side wall surface of the second conductive metal layer 12.
In such a conventional structure, the metal elements constituting the bump 4, tend to penetrate into the second conductive metal layer 12 in a lateral direction from the side surface thereof. This brings about a degradation in the barrier properties of the second conductive metal layer 12, and the second conductive metal layer 12 tends to become brittle of as a result of the lateral diffusion. In the worst case, the first and third conductive metal layers 11 and 13 may separate from each other at the second conductive metal layer.
Further, in the case where the second conductive metal layer 12 is formed of a material weak in the oxidation resistance, the exposed side wall surface thereof easily oxidized. When the side wall surface of the second conductive metal layer 12 is thus oxidized, the exposed wall surface is not covered by the molten solder alloy at the time of transferring the solder bump, due to the poor wetting of the oxide surface by the molten solder alloy. Thus the reliability of the bump 4 is degraded.
It is a general object of the present invention to provide a semiconductor device and a method for producing the same, in which the above disadvantages are eliminated.
Another and a more specific object of the present invention is to provide a semiconductor device and a method for producing the same, in which electrodes provided on a semiconductor substrate thereof and protruding electrodes can be connected with higher reliability.
Still another object of the present invention is to provide a semiconductor device comprising a semiconductor substrate; a plurality of electrode pads provided on said semiconductor substrate; a plurality of protruding electrodes, each corresponding to said electrode pad provided on said semiconductor substrate; and a plurality of barrier metal structures provided in correspondence to said electrode pads, each barrier metal structure including a plurality of deposited conductive metal layers for interconnecting said electrode pad to said protruding electrode; wherein an uppermost one of a plurality of said conductive metal layers of said barrier metal structure, which is in contact with said protruding electrode, covers an outer side wall of a conductive metal layer underlying said uppermost conductive layer.
Still another object of the present invention is to provide a method for producing a semiconductor device, comprising the step of a) forming a barrier metal structure which includes a plurality of deposited conductive metal layers on an electrode pad provided on a semiconductor substrate of said semiconductor device; and b) thereafter, forming a protruding electrode on said barrier metal structure; wherein said step a) further comprising the sub-steps of:xe2x80x94forming a first conductive metal coating on said semiconductor substrate, said first conductive metal coating being made of a material having a good adhesion with respect to said electrode;xe2x80x94forming a second conductive metal coating on said first conductive metal coating for connecting to said electrode electrically, said second conductive metal coating made of a material having a good adherence with said first conductive metal coating, said first and second metal coatings forming a first metal layer;xe2x80x94forming a second conductive metal layer which has an area at least including a forming area of said electrode pad by performing a patterning process only for said second conductive metal coating;xe2x80x94forming a third conductive metal coating made of a material having a good adherence with said second conductive metal layer and further with said protruding electrode, so as to cover at least said second conductive metal layer including a side wall part thereof; and pattering said first conductive metal layer while using said third conductive metal layer as a mask.
Other objects, features and advantages of the present invention will become more apparent from the following detailed description when read in conadherence with the accompanying drawings.